Fiber-reinforced resin molded article and method of manufacturing the same

ABSTRACT

A fiber-reinforced lightweight resin molded article with pores has a portion having a porosity lower than that of other general portions. Such a low-porosity portion serves as a rib in the resultant molded articles, to thereby enables to provide a fiber-reinforced lightweight resin molded article having excellent rigidity, bending strength, impact strength, uniformity of strength, resistance to local stress and torsion. The present invention also provides an efficient method for manufacturing the fiber-reinforced lightweight resin molded article.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fiber-reinforced resin molded articleand a method of manufacturing the same, and more specifically to alightweight resin molded article reinforced with glass fiber or likefibers, which has excellent rigidity, bending strength, impact strength,uniformity of strength, resistance to local stress and torsion, such asa fiber-reinforced resin molded article having a rib structure or arib-like structure in the interior of the molded article. The presentinvention also relates to an efficient method for manufacturing thesame.

2. Description of the Related Art

Conventionally, there has been known a fiber-reinforced resin moldedarticle reinforced by addition of fibers such as glass fiber. Since thefiber-reinforced resin molded article is excellent in mechanicalcharacteristics such as tensile strength and bending strength, and inheat resistance, it is widely used for automobile parts such as in-panecores, bumper beams, door steps, roof-racks, rear quarter panels, andair cleaner cases, and for construction/civil engineering materials suchas panels for external walls or partition walls, and cable troughs. Inmanufacture of these fiber-reinforced resin molded articles, there maybe employed an injection molding method for injecting a fiber-containingmolten resin into a cavity within molds. This injection molding methodenables molding of an article having an intricate shape, as well as massproduction of articles of the same shape since a predetermined moldingcycle can be repeated continuously.

When the amount of the fiber added to the fiber-reinforced resin moldedarticle manufactured through injection molding is increased in order toimprove the strength and rigidity thereof, the article tends to gainweight and suffer severe warp. For the purpose of reducing the weight ofthe molded articles, as well as solving other problems, Japanese PatentApplication Laid-Open (kokai) Nos. 7-247679, etc. disclose an expansioninjection molding method in which a foaming agent is added to resinmaterial and the material is foamed and molded into a molded article.However, in this expansion injection molding method, if a considerableamount of foaming agent is used for reducing the weight of the moldedarticle, a sufficient expansion ratio is not easily obtained. Even if asufficient expansion ratio is obtained, the appearance of the moldedarticle is impaired due to foaming, large pores are easily formed withinthe molded article, and uniform pores are not easily formed therein.Therefore, mechanical requirements such as strength, rigidity, andimpact resistance may not be sufficiently met, despite the moldedarticle containing fiber for reinforcement.

To solve the above-mentioned problems, and to reduce the weight ofmolded articles while maintaining the quality of appearance andmechanical characteristics such as strength, rigidity, and impactresistance of the molded article, the following techniques have beenproposed: (1) an expansion molding method in which fiber-reinforcedresin pellets containing relatively long fiber are melted into moltenresin and the molten resin is expanded during molding throughutilization of the springback phenomenon caused by the contained fiber,to thereby obtain a lightweight molded article; (2) an expansion moldingmethod in which a foaming agent for supplementing the expansion of resinis mixed into the fiber-reinforced resin pellets in item (1) above inorder to further reduce the weight of molded articles (InternationalPatent Publication WO97/29896). These methods sufficiently reduce theweight of molded articles without impairing the mechanicalcharacteristics thereof, and are effective in reduction of the weight offiber-reinforced resin molded articles.

As another method, there has been proposed (3) a method of manufacturingfoamed resin molded articles in which a molten resin containing achemical foaming agent is charged, through injection or injectioncompression, into the cavity of molds which comprise a movable corehaving a slit; the resin surface in contact with the mold is cooled andsolidified without foaming; the capacity of the cavity is expanded bymoving the movable core so as cause the molten resin to foam in theincreased capacity of the cavity, to thereby manufacture a foamed resinmolded article having a rib structure (Japanese Patent ApplicationLaid-Open (kokai) No. 9-104043).

However, depending on the degree of weight reduction (expansion) orshape of a molded article; for example, in such a case in which themolded article has a large region or capacity, the molded articleobtained through the above method (1) or (2) may have insufficientbending strength and rigidity, yet insufficient resistance to localstress, low uniformity of strength and resistance to torsion, requiringimprovements. In the above method (3) using a foaming agent, expansionof the foaming agent is difficult to suppress at the time of injection.Especially, during injection molding with compressed pressure, the resintends to foam at the time of injection due to reduction in resinpressure, resulting in silver marks on the surface of the resultantmolded article. Also, at a high expansion ratio, large pores are formedwithin the foamed portion as shown in the Examples herein, resulting ina molded article of poor uniformity. Moreover, even if reduction of theweight is achieved, molded articles having sufficient strength are noteasily obtained. Furthermore, since the foamed product comes to haveclosed cells, the cooling time of the resultant molded article isextended. As a result, the molding cycle is prolonged, which is aproblem in productivity.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a fiber-reinforcedresin molded article which has excellent bending strength, rigidity,impact strength, heat resistance, sufficient resistance to local stressand torsion, and uniformity.

Another object of the present invention is to provide a method ofmanufacturing such a resin molded article.

In view of the foregoing, the present inventors conducted carefulstudies on the overall structure—including the internal structure—offiber-reinforced lightweight resin molded articles with dispersed porestherein and the properties thereof. As a result, they found that, in aconventional method in which a movable core is simply retracted forexpansion, there is obtained a resin molded article having anon-expansion or low-expansion portion formed in the peripheral edgethereof, and near-uniform expansion occurs in other general portionssuch as the central portion thereof having a flat-shaped structure. Theyalso found that if a molded article has a coarse-and-dense structure interms of pores rather than the case in which pores are uniformlydispersed over the entirety of a molded article, and the molded articlealso has a unique rib-like structure by which a function of a rib isexerted between the two skin layers, the properties of the moldedarticle are improved.

In connection with the method of forming the above-mentioned rib orrib-like structure within a resin molded article, the present inventorsfound firstly that if a grooved portion is provided in the thicknessdirection of a uniformly expanded portion, the grooved portion serves asa structure equivalent to a rib having a low porosity. They also foundthat the structure is attained through a method in whichfiber-containing molten thermoplastic resin is injected into a cavityformed by a movable core which can advance and retract relative to thecavity of the mold and which has a protruding portion for forming agrooved portion of the molded article, and in which the movable core issubsequently retracted so as to expand the capacity of the cavity.

Secondly, they found that if a low- or non-expansion portion is formedthrough changing the degree of expansion relative to the uniformlyexpanded portion of the molded article having a substantially uniformthickness, the low- or non-expansion region advantageously comes tosubstantially serve as a rib structure. They also found that the moldedarticle having this structure can be manufactured through a moldingmethod in which only the regions corresponding to the movable portionsare expanded by use of a movable core which can advance and retractrelative to the cavity and which has a plurality of cavity moldingsurfaces (movable core having a plurality of movable portions).

Thirdly, the present inventors found that the properties of a moldedarticle are improved if the structure of a uniformly expanded portion ischanged so that the molded article attains a kind of rib structure inwhich substantially no or very few pores are formed in the thicknessdirection between the skin layers, and that such a molded article can bemanufactured through provision of a slit on the cavity side of themovable core.

Fourthly, the present inventors found that if a rib-like ordispersing-type protruding portion is formed on a uniformly expandedportion, the protruding portion exhibits reinforcement effects similarto those of a rib, and, in addition, that if a fiber-containing moltenresin (thermoplastic resin) is expanded, the region corresponding to theprotruding portion, i.e., the portion of the protruding portion plus theregion of the body thereunder, obtains a low-expanded, i.e.,low-porosity dense structure as compared to other flat portions. Theyalso found that the molded article having this structure can bemanufactured through a method in which fiber-containing molten resin isinjected into a specific mold cavity, and one mold is retracted towardthe direction in which the mold cavity is expanded.

Based on the above findings, the present inventors have accomplished thepresent invention. Accordingly, the present invention provides thefollowing:

(1) A fiber-reinforced lightweight resin molded article having pores,which comprises in the molded article a portion having a porosity lowerthan that of other general portions.

(2) The fiber-reinforced lightweight resin molded article according toitem (1) above, wherein the portion having a porosity lower than that ofother general portions is formed in the thickness direction of themolded article.

(3) The fiber-reinforced lightweight resin molded article according toitem (1) above, wherein the portion having a porosity lower than that ofother general portions has a rib structure or a rib-like structure.

(4) A fiber-reinforced lightweight resin molded article having pores,wherein a grooved portion is formed in the thickness direction of themolded article.

(5) A fiber-reinforced lightweight resin molded article according toitem (4) above, wherein a resin portion forming a grooved portion has aporosity lower than that of other flat portions.

(6) A fiber-reinforced lightweight resin molded article according toitem (4) or (5) above, wherein the molded article contains 10-70 wt. %glass fiber having a mean fiber length of 1-20 mm.

(7) A fiber-reinforced lightweight resin molded article according to anyof items (4)-(6) above, wherein a face material is integrally moldedwith the molded article.

(8) A method of manufacturing a fiber-reinforced lightweight resinmolded article having a grooved portion in the thickness direction ofthe molded article, which comprises the steps of injecting afiber-containing molten thermoplastic resin into a mold cavity formedwithin a mold having a movable core which can advance and retractrelative to the mold cavity and also having a protruding portion forforming a grooved portion in the molded article in the thicknessdirection of the molded article; and retracting the movable core towardthe direction in which the capacity of the mold cavity is expanded.

(9) A method of manufacturing a fiber-reinforced lightweight resinmolded article according to item (8) above, wherein a fiber-containingmolten thermoplastic resin is injected into a mold cavity formed by afixed mold, a moving mold having a protruding portion for forming agrooved portion of the molded article, and a movable core capable ofadvancing and retracting within the moving mold.

(10) A method of manufacturing a fiber-reinforced lightweight resinmolded article according to item (9) above, wherein at the time ofinjection a part of a mold cavity is defined by a gap between theprotruding portion of a moving mold and a movable core.

(11) A method of manufacturing a fiber-reinforced lightweight resinmolded article according to any of items (8)-(10) above, wherein a gasis injected into the interior of the fiber-reinforced lightweight resinmolded article within the mold cavity.

(12) A method of manufacturing a fiber-reinforced lightweight resinmolded article according to any of items (8)-(11) above, wherein afiber-containing molten thermoplastic resin is injected into the moldcavity on the surface of which a face material is applied in advance

(13) A method of manufacturing a fiber-reinforced lightweight resinmolded article according to any of items (8)-(12) above, wherein thefiber-containing molten thermoplastic resin is obtained by plasticizingand melting fiber-containing thermoplastic resin pellets having a lengthof 2-100 nm and contains parallel-arranged fiber having the same lengthin an amount of 20-80 wt. % with respect to the weight of the resultantresin-fiber mixture, or obtained by plasticizing and melting a mixtureof the pellets and other pellets containing fiber so that the amount offibers is 10-70 wt. % with respect to the weight of the entirety of themixture.

(14) A fiber-reinforced lightweight resin molded article containingpores, wherein portions other than the peripheral portion of the moldedarticle are composed of a plurality of regions having differentexpansion coefficients.

(15) A fiber-reinforced lightweight resin molded article according toitem (14) above, wherein portions other than the peripheral portion ofthe molded article are composed of a low expansion coefficient regionhaving an expansion coefficient of 1.0-1.5 and a high expansioncoefficient region having an expansion coefficient of 1.6-8.

(16) A fiber-reinforced lightweight resin molded article according toitem (14) or (15) above, wherein the fiber contained in the moldedarticle is glass fiber having a mean fiber length of 1-20 mm and thecontent thereof is 10-70 wt. %.

(17) A fiber-reinforced lightweight resin molded article according toany of items (14)-(16) above, wherein a face material is integrallymolded with the molded article.

(18) A method of manufacturing a fiber-reinforced lightweight resinmolded article, wherein a fiber-containing molten thermoplastic resin isinjected into a cavity corresponding to a clearance provided by amovable core which has a plurality of surfaces facing the cavity andwhich can advance and retract relative to the mold cavity, and then themovable core is retracted toward the direction in which the capacity ofthe mold cavity is expanded.

(19) A method of manufacturing a fiber-reinforced lightweight resinmolded article according to item (18) above, wherein a gas is injectedinto the interior of the fiber-containing molten thermoplastic resin inthe mold cavity.

(20) A method of manufacturing a fiber-reinforced lightweight resinmolded article according to item (18) or (19) above, wherein afiber-containing molten thermoplastic resin is injected into the moldcavity on the surface of which a face material is applied in advance.

(21) A method of manufacturing a fiber-reinforced lightweight resinmolded article according to any of items (18)-(20) above, wherein thefiber-containing molten thermoplastic resin is obtained by plasticizingand melting fiber-containing thermoplastic resin pellets having a lengthof 2-100 mm and contains parallel-arranged fiber having the same lengthin an amount of 20-80 wt. % with respect to the weight of the resultantresin-fiber mixture, or obtained by plasticizing and melting a mixtureof the pellets and other pellets containing fiber so that the amount offibers is 10-70 wt. % with respect to the weight of the entirety of themixture.

(22) A fiber-reinforced resin molded article comprising skin layers, afiber-containing coarse region having substantially continuous pores,and a fiber-containing dense region having substantially no continuouspores, wherein the dense region constitutes a rib structure whichbridges the skin layers.

(23) A fiber-reinforced resin molded article according to item (22)above, wherein the fiber-containing coarse region has a porosity of50-90% and the fiber-containing dense region has a porosity of 0-30%.

(24) A fiber-reinforced resin molded article according to item (22) or(23) above, wherein the fiber contained in the molded article is glassfiber having a mean fiber length of 1-20 mm and the content thereof is10-70 wt. %.

(25) A fiber-reinforced resin molded article according to any of items(22)-(23) above, wherein a face material is integrally molded with themolded article.

(26) A method of manufacturing a fiber-reinforced resin molded articlecomprising a rib structure, wherein a fiber-containing molten resin isinjected or compression-injected into a cavity formed by molds includinga movable core which has a slit in communication with the cavity, andthen the movable core is retracted toward the direction in which thecapacity of the mold cavity is expanded.

(27) A method of manufacturing a fiber-reinforced resin molded articleaccording to item (26) above, wherein the cavity is formed by a fixedmold, a moving mold., and a movable core which can advance and retractwithin the moving mold relative to the mold cavity.

(28) A method of manufacturing a fiber-reinforced resin molded articleaccording to item (26) or (27) above, wherein a gas is injected into theinterior of the fiber-containing molten resin in the cavity after thestart of retracting of the movable core.

(29) A method of manufacturing a fiber-reinforced resin molded articleaccording to any of items (26)-(28) above, wherein a fiber-containingmolten resin is injected or compression injected into the cavity, on thesurface of which a face material is applied in advance.

(30) A method of manufacturing a fiber-reinforced resin molded articleaccording to any of items (26)-(29) above, wherein the fiber-containingmolten thermoplastic resin is obtained by plasticizing and meltingfiber-containing thermoplastic resin pellets having a length of 2-100 mmand contains parallel-arranged fiber having the same length in an amountof 20-80 wt. % with respect to the weight of the resultant resin-fibermixture, or obtained by plasticizing and melting a mixture of thepellets and other pellets containing fiber so that the amount of fibersis 10-70 wt. % with respect to the weight of the entirety of themixture.

(31) A fiber-reinforced lightweight resin molded article comprising aprotruding portion, wherein the molded article contains pores and has aprotruding portion on at least one of the surfaces extendingperpendicularly to the thickness direction of the molded article, andthe porosity of the region corresponding.to the protruding portion islower than that of other flat portions.

(32) A fiber-reinforced lightweight resin molded article comprising aprotruding portion according to item (31) above, wherein the porosity ofthe region corresponding.to the protruding portion is 0.1-60% and thatof other flat portions is 30-90%.

(33) A fiber-reinforced lightweight resin molded article according toitem (31) or (32) above, wherein the fiber contained in the moldedarticle is glass fiber having a mean fiber length of 1-20 mm and thecontent thereof is 10-70 wt. %.

(34) A fiber-reinforced lightweight resin molded article according toany of items (31)-(33) above, wherein a face material is integrallymolded with the molded article.

(35) A method of manufacturing a fiber-reinforced lightweight resinmolded article comprising a protruding portion, wherein afiber-containing molten resin is injected into a cavity formed by a pairof molds, one of which has a grooved portion for forming a protrudingportion, and then one of the molds is retracted toward the direction inwhich the capacity of the mold cavity is expanded, whereby the porosityof the region corresponding to the protruding portion is lower than thatof other flat portions.

(36) A method of manufacturing a fiber-reinforced lightweight resinmolded article comprising a protruding portion according to item (35)above, wherein a gas is injected into the interior of thefiber-containing molten resin in the cavity.

(37) A method of manufacturing a fiber-reinforced lightweight resinmolded article according to item (35) or (36) above, wherein afiber-containing molten resin is injected into the cavity on the surfaceof which a face material-is applied in advance.

(38) A method of manufacturing a fiber-reinforced lightweight resinmolded article comprising a protruding portion according to any of items(35)-(37) above, wherein the fiber-containing molten thermoplastic resinis obtained by plasticizing and melting fiber-containing thermoplasticresin pellets having a length of 2-100 mm and contains parallel-arrangedfiber having the same length in an amount of 20-80 wt. % with respect tothe weight of the resultant resin-fiber mixture, or obtained byplasticizing and melting a mixture of the pellets and other pelletscontaining fiber so that the amount of fibers is 10-70 wt. % withrespect to the weight of the entirety of the mixture.

According to the present invention, there is provided a fiber-reinforcedresin molded article which has excellent bending strength, rigidity,impact resistance, heat resistance, sufficient resistance to localstress and torsion, and uniformity. Also, in the method of manufacturingthe same according to the present invention, reduction in the weight ofa molded article can be arbitrarily regulated by use of molds havingrelatively simple structure, and the excellent surface quality of amolded article can be obtained, for example, the flat structure of theexterior of a highly lightweight molded article can be maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a first embodiment of the method ofmanufacturing a fiber-reinforced lightweight resin molded article of afirst mode in the present invention, wherein FIG. 1(A) shows a conditionimmediately before expansion of the cavity of the injection mold, andFIG. 1(B) shows a condition after the expansion.

FIG. 2 schematically shows the second embodiment of the method ofmanufacturing the fiber-reinforced lightweight resin molded article ofthe first mode in the present invention, wherein FIG. 2(A) shows acondition before expansion of the cavity of the injection mold, and FIG.2(B) shows a condition after the expansion.

FIG. 3 schematically shows the third embodiment of the method ofmanufacturing the skin-integrated, fiber-reinforced lightweight resinmolded article of the first mode in the present invention, wherein FIG.3(A) shows a condition before expansion of the cavity of the injectionmold, and FIG. 3(B) shows a condition after the expansion.

FIG. 4 schematically shows the first embodiment of the method ofmanufacturing the fiber-reinforced resin molded article of the secondmode in the present invention, wherein FIG. 4(A) shows a conditionbefore expansion of the cavity of the injection mold, and FIG. 4(B)shows a condition after the expansion.

FIG. 5 schematically shows the second embodiment of the method ofmanufacturing the skin-integrated, fiber-reinforced resin molded articleof the second mode in the present invention, wherein FIG. 5(A) shows acondition before expansion of the cavity of the injection mold, and FIG.5(B) shows a condition after the expansion.

FIG. 6 schematically shows the first embodiment of the method ofmanufacturing a fiber-reinforced resin molded article of the third modein the present invention, wherein FIG. 6(A) shows a condition beforeexpansion of the cavity of the injection mold, and FIG. 6(B) shows acondition after the expansion.

FIG. 7 schematically shows the second embodiment of the method ofmanufacturing the skin-integrated, fiber-reinforced resin molded articleof the third mode in the present invention, wherein FIG. 7(A) shows acondition before expansion of the cavity of the injection mold, and FIG.7(B) shows a condition after the expansion.

FIG. 8 schematically shows the first embodiment of the method ofmanufacturing the fiber-reinforced resin molded article of the fourthmode in the present invention, wherein FIG. 8(A) shows a conditionbefore expansion of the cavity of the injection mold, and FIG. 8(B)shows a condition after the expansion.

FIG. 9 schematically shows the second embodiment of the method ofmanufacturing a fiber-reinforced resin molded article of the fourth modein the present invention, wherein FIG. 9(A) shows a condition beforeexpansion of the cavity of the injection mold, and FIG. 9(B) shows acondition after the expansion.

FIG. 10 schematically shows the third embodiment of the method ofmanufacturing the skin-integrated, fiber-reinforced resin molded articleof the fourth mode in the present invention, wherein FIG. 10(A) shows acondition before expansion of the cavity of the injection mold, and FIG.10(B) shows a condition after the expansion.

FIG. 11 schematically shows the fourth embodiment of the method ofmanufacturing the skin-integrated, fiber-reinforced article of thefourth mode in the present invention, wherein FIG. 11(A) shows acondition immediately before expansion of the cavity of a mold forintegrally molding a resin and a face material, FIG. 11(B) shows acondition after the expansion, and FIG. 11(C) is a sectional view of amolded article manufactured according to the fourth embodiment of thefourth mode in the present invention, which shows the distribution ofpores formed therein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will next be described in detail.

The present invention provides a fiber-reinforced lightweight resinmolded article which has a portion having a porosity lower than that ofother flat (or general) portions; more specifically, a rib or rib-likestructure in the interior of the molded article which contains porestherein, more specifically, a rib or rib-like structure in the thicknessdirection of the molded article. The present invention includes fourspecific modes for the molded article and methods suitable formanufacturing the respective modes as follows:

First Mode

A first mode of the present invention is directed to a fiber-reinforcedlightweight resin molded article having therein pores, specificallydispersed pores, and a grooved portion in the thickness direction of themolded article, and more specifically to a fiber-reinforced lightweightresin molded article wherein a resin portion forming the grooved portionhas a porosity lower than that of other flat portions. The first mode ofthe present invention is also directed to a method of manufacturing sucha fiber-reinforced lightweight resin molded article in an efficientmanner.

In manufacture of the fiber-reinforced lightweight resin molded articlehaving dispersing pores therein, a fiber-containing molten resin(thermoplastic resin) is injected or compression-injected into a moldcavity in order to fill the cavity with the resin, and then the moldcavity is expanded to the volume of a desired molded article. At thistime, the molten resin is expanded to the desired volume by virtue ofthe springback phenomenon caused by tangled fibers contained therein.After cooling, the mold is opened, and there is obtained afiber-reinforced lightweight resin molded article having dispersed porestherein.

The manufacturing method of the first mode is characterized in that afiber-containing molten resin is injected into a mold cavity formed by amold having a protruding portion for forming a grooved portion in themolded article, and then a movable core is retracted, while theprotruding portion remains at its position, so as to expand the cavity,thereby completing the molding.

In the general case where a single movable core having a simple shape,i.e., a surface shape identical with that of the entire cavity surface(in a flat shape) is used, there is obtained a fiber-reinforcedlightweight resin molded article having a near-uniform expansioncoefficient. Although the molded article is light, it has a larger areaand volume. When the weight of the molded article is reduced further,the article may not attain sufficient strength and rigidity. Incontrast, in the case in which there is used a movable core such that agap exists between core and the side wall of a mold cavity, there isobtained a high-expansion-coefficient molded article which has aperipheral portion of non- or low expansion, and other non-peripheralportions, i.e., the central portion, are of uniform expansion. Sincethis molded article attains an unexpanded skin layer on its surface incontact with the wall of the molds under cooling, the molded article islightweight and has high strength and rigidity. However, such a moldedarticle having a three-layered structure composed of a skin layer/anexpansion layer/a skin layer may fail to attain sufficient rigidity whenits area and volume are large, and may have insufficient resistance tolocal stress and torsion.

In order to solve these problems, in the first mode, the skin layers onthe two surfaces are partially connected via a non- or low-expansionresin. Therefore, in the manufacturing method according to the firstmode, a fiber-containing molten thermoplastic resin is injected into amold cavity formed by a movable core having a protruding portion forforming a grooved portion of a molded article, and then the movable coreis retracted toward the direction in which the mold cavity is expanded.

The shape and number of core(s) are properly determined according to thesize and desired features of the molded article. The location, shape,size, number, distribution, etc. of the protruding portion(s) forforming the grooved portion are arbitrarily determined as appropriate inconsideration of the shape, thickness, area, volume, degree of weightreduction, environment of use, and desired performance of the moldedarticle. Generally, the grooved portion is provided in the reversesurface of the molded article and has a width of about 2-10 mm and alength of 10 mm or more. Preferably, the grooved portion is continuouslyor intermittently formed in any direction. The resin layer between thebottom surface of the grooved portion and the molded article surface atthe opposite side is preferably a resin layer having substantially no orvery few pores. Generally, the mold having the protruding portion forforming the grooved portion is a moving mold, and a movable core whichcan advance and retract therewithin and a fixed mold form a mold cavity.With this protruding portion provided in the movable core, injection ofa molten resin and retraction of the movable core can be performed whilethe protruding portion is thrust into the cavity, and the cavity can beexpanded to a predetermined volume while the protruding portion is fixedin position. Therefore, within a certain range of weight reduction,another protruding portion can be provided in the fixed mold facing themovable core.

In the case in which a protruding portion is provided in the movingmold, the disposition of molds is designed such that a movable core canadvance and retract within the moving mold having the protrudingportion. Also, a gap may be provided in the protruding portion facingthe movable core so that the gap forms a part of the mold cavity at thetime of injection of a molten resin. With this structure, the shape ofthe surface of the protruding portion facing the cavity is transferredto a finished molded article so that the influence exerted by thesubsequent retraction of the movable core is eliminated, and the skinlayers are formed to be firm. Likewise, the position of the protrudingportion when thrust into the mold cavity and that of the movable corewhen thrust into the same are determined as appropriate. Generally, theyare determined so as to provide an appropriate clearance between theprotruding portion and the surface of the mold facing thereto.

Second Mode

Next will be described a second mode of the present invention.

The second mode is directed to a fiber-reinforced lightweight resinmolded article having pores, specifically dispersed pores, wherein theportions other than the peripheral portion of the molded article arecomposed of a plurality of regions having different expansioncoefficients. The second mode of the present invention is also directedto a method of manufacturing such a fiber-reinforced lightweight resinmolded article in an efficient manner.

The molded article is manufactured through a molding method in which aresin is expanded to the expanded portion of the mold cavity provided bythe retraction of a movable core which can advance and retract relativeto the cavity and which has a plurality of surfaces facing the cavity.

To solve the above-mentioned problem relating to the use of a singlemovable core having a simple shape, in the manufacture method of thesecond mode, the skin layers on the two surfaces of the molded articleare partially connected via a non- or low-expansion layer. Therefore, inthe manufacture method according to the second mode, a fiber-containingmolten thermoplastic resin is injected into a mold cavity, which is aclearance formed by the cavity-forming surface of a movable core thrustinto the cavity, which has a plurality of surfaces (a plurality ofmovable portions) facing the cavity and can advance and retract relativeto the mold cavity, and then the movable core is retracted toward thedirection in which the mold cavity is expanded.

The shape and number of a plurality of the movable cores for forming acavity-forming surface are properly determined according to the size anddesired features of the molded article. Likewise, the positions of aplurality of the movable cores when thrust into the cavity aredetermined as appropriate. Generally, the position is determined so asto provide a proper clearance between the movable cores and another moldfacing thereto in consideration of the expansion coefficient of themolded article.

Third Mode

Next will be described a third mode of the present invention.

The third mode is directed to a fiber-reinforced resin molded articlecomprising skin layers, a coarse fiber-containing region havingsubstantially continuous pores, and a dense fiber-containing regionhaving substantially no continuous pores, wherein the dense regionconstitutes a rib structure which bridges the skin layers. The thirdmode of the present invention is also directed to a method suitable formanufacturing such a fiber-reinforced resin molded article.

In the third mode, a fiber-reinforced lightweight resin molded articlehaving dispersed pores is manufactured through utilization of thespringback phenomenon caused by tangled fibers contained in the moltenresin by use of a set of molds including a movable core which has a slitin communication with a mold cavity. That is, the fiber-containingmolten resin is injected or compression-injected into the mold cavity soas to charge the resin in the cavity. When the charged resin enters theslit where cooling is intense, the flowability of the resin is loweredor lost. Subsequently, the movable core is retracted to the positionwhich provides the volume of the finished molded article, and the resinis then expanded due to the above-mentioned springback phenomenon,followed by cooling, to thereby obtain a fiber-reinforced lightweightresin molded article having pores therein.

Meanwhile, the resin within the slit has been subjected to cooling andtransfer of the mold shape. When the movable core is retracted, theresin is released from the movable core and remains in the interior ofthe cavity. Therefore, the resin within the slit is substantiallyunexpanded. Even if the resin is expanded, the degree of expansion isvery low, and thus under normal conditions there occurs no expansionproviding continuous pores, resulting in the formation of a denseregion. The resin within the slit constitutes a rib structure whichconnects the skin layers on the two sides of the molded article. Thisstructure improves the strength, rigidity, uniformity of strength, andresistance to torsion in a molded article having larger area and volume,while achieving reduction of the weight of the molded article.

To solve the above-mentioned problems relating to the use of a singlemovable core having a simple shape, in the manufacturing method of thethird mode, the skin layers on the two surfaces of the molded articleare partially connected via a dense resin region having a substantiallylow porosity.

Therefore, in the manufacturing method according to the third mode, afiber-containing molten resin is injected or compression-injected into amold cavity so as to charge the resin in the cavity formed by a set ofmolds including a movable core which has a slit in communication withthe cavity and which can advance and retract relative to the moldcavity, and then the movable core is retracted for expansion of theresin to the position which provides the volume of the finished moldedarticle, with the resin-within the slit being maintained in the cavityafter being cooled.

The volume of the cavity when the resin is injected orcompression-injected therein so as to charge the resin in the cavity isdetermined such that it is smaller than the volume of the finishedmolded article, in consideration of the thickness and weight reduction(expansion coefficient) of the finished molded article. The initial moldcavity can be formed by a movable core having a slit in communicationwith a fixed mold and cavity. Preferably, however, it also comprises amoving mold in addition to the movable core and has a mold structuresuch that the movable core can advance and retract within the movingmold.

The shape of the movable core is properly determined according to thesize and desired features of the molded article. The location, shape,size, number, distribution, etc. of the slit(s) provided in the movablecore are arbitrarily determined as appropriate in consideration of theshape, thickness, area, volume, degree of weight reduction, environmentof use, and desired performance of the molded article. Typically, atleast one slit is provided in the central portion of the molded article,having a shape of a groove having a width of about 1-10 mm and a lengthof 10 mm or more. Preferably, the slit is continuously or intermittentlyformed in any direction. The depth of the slit in the thicknessdirection is about the same as that of the molded article or slightlylarger in some cases. The mold is preferably cooled in such a mannerthat the slit of the movable core is cooled intensely. A protrudingportion formed on a fixed mold corresponding to the slit of the movablecore can promote cooling at the entrance of the slit and enhance the ribstructure effects, depending on the thickness of the initial cavity.

The molds are preferably formed of a fixed, movable, and moving moldssince the degree of freedom of molding conditions is secured and themolded article is easily released. Therefore, the mold cavity is formedof a moving mold, a movable core which can advance and retract withinthe moving mold, and a fixed mold. In this case, the portions of thecavity other than the slit may be approximately flat. A gap may beprovided between the moving mold and the movable core so that the gapforms a part of the mold cavity at the time of injection of a moltenresin. With this structure, the shape of the surface of the peripheraledge of the cavity is transferred to the peripheral edge of a finishedmolded article when molten resin is injected or compression-injectedinto the mold cavity. Thus, the subsequent retraction of the movablecore hardly causes expansion, with the shape being maintained, resultingin the firm formation of a dense region in the peripheral edge as well.

Fourth Mode

Next will be described a fourth mode of the present invention.

The fourth mode is directed to a fiber-reinforced lightweight resinmolded article containing therein pores, specifically dispersed pores,and having a protruding portion on at least one surface in the thicknessdirection of the molded article, and wherein a region corresponding tothe protruding portion has a porosity lower than that of other portions.The fourth mode of the present invention is also directed to a methodsuitable for manufacturing such a fiber-reinforced resin molded article.

The fourth mode is characterized in that, when pores are formed byexpansion of a molten resin to the volume of a mold cavity by virtue ofthe springback phenomenon caused by tangled fibers contained therein, afiber-containing molten resin is injected into a mold cavity having agrooved portion to form a protruding portion on at least a surface inthe thickness direction of the molded article having a flat-shapestructure, and a mold is retracted to a direction that expands the moldcavity. Thus, the region corresponding to the protruding portion of themolded article has a porosity lower than that of other portions.

When a cavity having a flat shape is used, there is obtained afiber-reinforced lightweight resin molded article having a near-uniformexpansion coefficient (porosity). In contrast, in the case in whichthere is used a movable core such that a gap exists between the movablecore and the sidewall of a mold cavity, there is obtained a moldedarticle which has a peripheral portion of non- or low expansion, andother non-peripheral portions, i.e., the central portion, are of uniformhigh expansion. Since this molded article attains an unexpanded skinlayer on the surface thereof in contact with the wall of the molds undercooling, the molded article is lightweight and has high strength andrigidity. However, this molded article having a three-layered structurecomposed of a skin layer/an expansion layer/a skin layer in thethickness direction may fail to attain sufficient rigidity when its areaand volume are large, and may have insufficient resistance to localstress and torsion.

To solve these problems, in the fourth mode, the skin layers on the twosurfaces are partially connected via a non- or low-expansion resin.Therefore, in the manufacturing method according to the fourth mode, afiber-containing molten resin is injected into a mold cavity, which is aclearance formed by a movable core that can advance and retract relativeto the mold cavity, and which has a grooved portion for forming aprotruding portion in the thickness direction of the molded article, andin which the movable core is subsequently retracted so as to expand thecavity.

The location, shape, size, number, distribution, etc. of the groovedportion(s) for forming the protruding portion(s) are arbitrarilydetermined as appropriate in consideration of the shape, thickness,area, volume, degree of weight reduction, environment of use, anddesired performance of the molded article. The grooved portion isprovided on at least either a fixed or movable core forming the moldcavity, and may be provided on both fixed and movable cores atcorresponding locations on both surfaces or at other locations. Theprotruding portion can be provided continuously in the peripheral edgeof the molded article as well, thus improving the appearance of theperipheral portion of the molded article. Generally, however, since amolded article desirably has a smooth top surface, the protrudingportion is preferably provided in the reverse surface of the moldedarticle. The shape of the protruding portion is preferably rib-shaped soas to maximize its effect. Therefore, the protruding portion istypically provided in the reverse surface of the molded article, and hasa width of about 2-20 mm and a length of 10 mm or more. Preferably, theprotruding portion is continuously or intermittently formed in anydirection. In the manufacturing method according to the fourth mode,surprisingly, a fiber-containing molten resin expands at different ratesin the region corresponding to the grooved portion formed on the moldcavity and in other portions; that is, expansion in the grooved portion,i.e. a thick portion of the molded article, is suppressed thus impartinga function as a rib to the protruding portion of the molded article aswell as enhancing its rib effect due to a low porosity in the thicknessdirection even in the central portion of the molded article and a denserstructure thereof compared with other portions.

In the method of manufacturing a fiber-reinforced lightweight resinmolded article according to any of the modes described above, gas suchas nitrogen can be injected into a fiber-containing molten resin in thecavity at any time between the initiation and termination of expansionof the mold cavity or after the termination thereof. The injection ofgas promotes expansion of the fiber-containing molten resin, to therebypress the molten resin firmly against the molding surface of the moldedarticle. Thus, since resin is cooled in close contact with the surfaceof the mold, no sink marks are formed on the surface of the moldedarticle. In the third mode of the present invention, adhesion between adense region of the slit and resin contained in a coarse region, whichis an expanded portion, is expected to improve. Also, circulation of gasin the mold promotes cooling of the molded article, resulting inshortening of the molding cycle. In this case, addition of volatileliquid such as water can further enhance the cooling effect.

Also, the prior application of a face material may provide afiber-reinforced lightweight resin molded article which is integrallymolded with the face material. In the case in which a face material isintegrally molded with a molded article, the face material is generallyapplied onto the fixed mold surface. In the case of a molded articlewhose surface is covered with a face material, a resin is injectedthrough a side gate. For example, a grooved portion is generally formedin the resin surface behind the face material.

In the methods of the respective modes of the present invention, thefiber-containing molten resin is preferably a fiber-containing moltenresin in the form of pellets having a length of 2-100 mm containingparallel-arranged fiber having the same length in an amount of 20-80 wt.%, or a mixture of such pellets and other pellets containing fiber in anamount of 10-70 wt. %, which is plasticized and melted.

In this context, the other pellets may typically be pellets of athermoplastic resin, those containing any of various additives, thosecontaining no fiber, or those obtained through melt-kneading of glassfiber and the like.

The other pellets described above maintain the fiber contained in amolten thermoplastic resin for a long time, and improve thedispersibility thereof during injection molding.

The materials selected as above provide a strong springback phenomenon.In other words, the glass fiber contained in a molten thermoplasticresin is maintained for a long time, and the dispersibility thereof isimproved during molding. A small amount of a foaming agent (3 wt. % orless) may be added to the material resin, in order to compensate thedeficiency of expansion.

In reduction of the weight of the fiber-reinforced lightweight resinmolded article of the respective modes of the present invention, theoverall expansion coefficient is selected within the range of 1.5-8,varying with the type of the fiber contained in the resin, contentthereof, and required features of the desired molded article. If theexpansion coefficient is less than 1.5, the effects rendered by theweight reduction are low, whereas if the expansion coefficient is inexcess of 8, the surface smoothness of the molded article is lowered,the dense skin layers on the surfaces becomes thinner, and the strengthis lowered.

The mean porosity is about 30-90%, preferably about 33-88%. If the meanporosity is 30% or less, the effects rendered by the weight reductionare low, whereas if the mean porosity is in excess of 90%, the surfacesmoothness of the molded article is lowered, the dense skin layers onthe surfaces become thinner, and the strength is lowered.

The resin region of the molded article forming a rib has a porositylower than that of other flat portions. Among the pores, those not incommunication with other pores account for 0-30%.

In the first mode of the present invention, the porosity of the resinforming the protruding portion of the molded article is preferably lowerthan that of other flat portions.

In the fourth mode, the region corresponding to the protruding portionof the fiber-reinforced lightweight resin molded article has a porosityof 0.1-60%, and other flat portions have a porosity of 30-90%. Theseporositys are easily attained through regulation of the cavity volume atthe time of injection of molten resin, and the degree of expansion ofthe resin obtained through expansion of the cavity volume to the volumeof the finished molded article.

The mean length of the glass fiber contained in the molded article is1-20 mm, preferably 2-15 mm. If the mean length is less than 1 mm, theentanglement of the fibers and degree of the expansion becomeinsufficient, which is disadvantageous in terms of strength, rigidity,and impact resistance. If the mean length is in excess of 20 mm, thedispersibility and flowability of the fiber become insufficient at thetime of melting, and thus the resin does not easily flow into athin-wall portion such as s slit or a tip-end portion of the molds,which may result in defects in appearance or deteriorated moldability.

In the case in which glass fiber is used, the content is generally 10-70wt. %, preferably 15-60 wt. %. If the content is less than 10 wt. %, theexpansion, strength, rigidity, and heat resistance are not sufficient,whereas if the content is in excess of 70 wt. %, the flowability isdecreased at the time of melting, which may result in defects inappearance, or deteriorated expansion or moldability.

In this context, the expansion coefficient refers to “volume afterexpansion/volume without pores before expansion,” and the porosity (%)to “(volume of molded article—volume without pores (volume beforeexpansion)/volume of molded article)×100.”

In the other flat coarse portions, the porosity of pores communicatingwith other pores is 50-90%. The term “volume of the molded article” mayencompass a partial portion of the mold.

The thermoplastic resins usable in the respective modes of the presentinvention are not particularly limited, and there may be used polyolefinresins such as polypropylene, propylene-ethylene block copolymer,propylene-ethylene random copolymer, and polyethylene; polystyreneresins; ABS resins; polyvinyl chloride resins; polyamide resins;polyester resins; polyacetal resins; polycarbonate resins; polyaromaticether resins; polyaromatic thioether resins; polyaromatic ester resins;polysulfone resins; and acrylate resins.

Of these thermoplastic resins, there may be preferably usedpolypropylene resins such as polypropylene, block copolymer or randomcopolymer of polypropylene and another olefin, and mixtures thereof;polyamide resins; polyester resins; and polycarbonate resins; morepreferably polypropylene resins containing an acid-modified polyolefinresin modified with unsaturated carboxylic acid or a derivative thereof.

The usable fiber include ceramic fibers such as boron fiber, siliconcarbonate fiber, alumina fiber, silicon nitride fiber, zirconia fiber;inorganic fibers such as glass fiber, carbon fiber, metallic fiber,copper fiber, brass fiber, steel fiber, stainless steel fiber, aluminumfiber, and aluminum alloy fiber; organic fibers such as polyester fiber,polyamide fiber, aramid fiber, and polyarylate fiber; among which glassfiber is preferably used.

As the material of the fiber-containing thermoplastic resin, there arepreferably used fiber-containing thermoplastic resin pellets having alength of 2-100 mm and containing parallel-arranged fiber having thesame length in an amount of 20-80 wt. %, or a mixture of such pelletsand other pellets containing fiber in an amount of 10-70 wt. %. Whenpellets containing parallel-arranged fiber in an amount of 20-80 wt. %are plasticized, melted, or kneaded, the fibers contained therein arenot easily ruptured, and excellent dispersibility is maintained. Withthe above-mentioned pellets, the springback phenomenon caused by thefiber-containing molten resin in the cavity is intensified, the lengthof fibers retained in the finished molded article is lengthened, and theproperties and appearance of the surface of the molded article areimproved. As the plasticizing screw for injection molding, there ispreferably used a plasticizing screw providing a relatively lowexpression coefficient, in view of suppression of rupture of fibers.

As the glass fiber, there are used glass fibers of E-glass, S-glass, orlike glass having a mean fiber diameter of 25 μm or less, preferably3-20 μm. If the fiber diameter is less than 3 μm, the glass fiber is notcompatible with the resin during production of pellets, and thus theresin is not easily impregnated with the fiber. In contrast, if thefiber diameter is in excess of 20 μm, the appearance is deteriorated,fibers do not easily flow into a minute portion such as a rib, and theybecome susceptible to rupture and damage. In manufacture of pelletsthrough a pultrusion molding method by use of the above-mentionedthermoplastic resin and glass fiber, the glass fiber is subjected tosurface treatment with a coupling agent, and are formed into bundles of100-10000 fibers, preferably 150-5000 fibers, via a binder.

The coupling agent may be selected as adequate from among conventionalsilane and titanium coupling agents. For example, there may be usedaminosilane and epoxysilane such as γ-aminopropyltriethoxysilane,N-β-(aminoethyl)-γ-aminopropyltriethoxysilane,γ-glycidoxypropyltrimethoxysilane, andβ-(3,4,epoxycyclohexyl)ethyltrimethoxysilane. Most preferably, theabove-mentioned aminosilane compounds are used.

As the binder, there may be used a urethane binder, an olefin binder, anacrylic binder, a butadiene binder, or an epoxy binder. Of thesebinders, a urethane binder and an olefin binder are preferably used. Asthe urethane binder, there may be used either a one-component binder ofoil-modified type, moisture-setting type, block-type, or a like type; ora two-component binder of catalyst-setting type, polyol-setting type, ora like type, so long as the urethane binder contains polyisocyanatewhich is obtained through polyaddition of diisocyanate and polyhydricalcohol. As the olefin binder, there may be used an acid-modifiedpolyolefin resin modified with unsaturated carboxylic acid or aderivative thereof.

The fiber-containing resin pellets are manufactured throughapplication/impregnation of the thermoplastic resin to the glass fiberbonded together with the above-mentioned binder. The methods ofapplication/penetration of the glass fibers to the thermoplastic resininclude a method in which bundles of fibers are passed through moltenresin so as to impregnate the fibers with the resin, a method in whichfibers are impregnated with molten resin adhering to the fibers whilethe molten resin is expanded with a die, or a like method. Further, inorder to facilitate impregnation of the resin with fibers, i.e., inorder to improve the wetting of the fibers, there may be employed apultrusion molding method in which bundles of fibers under tension arepassed through and pulled out from the interior of a die whose innercircumferential edge has projections and depressions; and the bundles offibers are then passed through pressurized rollers in an additionalstep. If the glass fibers are easily soaked with the resin to be wet,the above-mentioned step of binding the fibers into bundles may beomitted, since the glass fibers are impregnated with the molten resinwith ease, resulting in simplified manufacture of pellets. In this case,in order to facilitate the soaking, there may be effectively employed amethod in which polarity is imparted to the resin, and a method in whichfunctional groups reactive with a coupling agent are grafted on to thesurfaces of the glass fibers.

Long fiber bundles (strands, etc.) impregnated with resin through thesemethods are cut along the width direction, to thereby obtain resinpellets which contain long fibers having the same length as the pellets.In this case, the resin pellets are not limited to those obtainedthrough a method in which resin-containing long fiber bundles having asubstantially circular lateral section are cut, and there may be usedthose obtained through a method in which resin-containing long fiberbundles in the form of a sheet, tape, or band containing flatly-arrangedfibers are cut to a predetermined length.

The above-mentioned material resin may contain a foaming agent in anamount of 3 wt. % or less.

The foaming power of the foaming agent contained in the materialcompensates for the deficiency of restoration force (expansion) offibers, when the restoration force (expansion) is insufficient in thespringback phenomenon. As a result, the fiber-containing moltenthermoplastic resin is reliably expanded to the volume of the moldedarticle corresponding to the retraction of the movable core.

When the foaming agent is contained in an amount in excess of 3 wt. %,there may result generation of silver marks, defects in appearance, andlarge hollows within the molded article, resulting in considerablylowered strength and rigidity.

For these reasons, the content of the foaming agent is preferablyreduced to as low as possible. Specifically, the content is 0.01-3 wt.%.

In this case, the type of the foaming agent is not particularly limited,so long as it is decomposed to generate a gas, and there may be usedoxalic acid derivative, azo compound, hydrazin derivative, semicarbazidecompound, azide compound, nitroso compound, triazole, urea, relatedcompounds of these listed, nitrite salt, hydride, carbonate salt, andbicarbonate salt. More specifically, there may be used azodicarbonamide(ADCA), benzenesulfohydrazide, N,N-dinitropentamethylenetetramine, andterephthal azide. Also, as needed, there may be added thereto a fillersuch as a stabilizer, antistatic agent, weather resistant agent, shortfibers, or talc.

As the gas injected into the fiber-containing molten thermoplastic resinin the cavity, there is preferably used a cooling gas at 15° C. or less,preferably 0° C. or less.

Also, the gas may be fed into the fiber-containing molten resin througha gas nozzle disposed in the nozzle of an injection apparatus forplasticizing and injecting the fiber-containing molten resin, or througha gas pin disposed in the sprue, runner, or cavity provided within themolds.

Of these gas nozzles and pins, preferably a gas pin provided within themolds, more preferably that disposed in the cavity, is used forinjection of the gas.

The pressure of the gas is 0.01-20 MPa, more preferably 0.1-5 MPa, mostpreferably 0.5-2 MPa. The pressure of the gas is determined according tothe size, shape, and expansion coefficient of the molded article; theflowability, viscosity, and fiber content of the molten resin; theshapes of the molds; and like factors. Generally, when the pressure ofthe gas is lowered, generation of large hollows within the molten resinis suppressed, and the strength is reliably secured. As a result, thegas does not easily enter the space between the molten resin surface andthe mold surface, and defects such as generation of silver marks arethus suppressed.

As mentioned above, the gas can be injected under a relatively lowpressure. This is because a great number of pores communicating with oneanother are retained within the molded article through utilization ofthe springback phenomenon caused by the fibers.

In contrast, since only isolated cells are formed in the process ofreduction in the weight of conventional short-fiber-containing resinthrough addition of a foaming agent, expansion of the isolated cells isnecessary for injection of a predetermined amount of the gas, i.e., ahigh-pressure gas is required rather than a low-pressure gas, resultingin large hollows.

That is, whether the method of weight reduction is achieved by means oflarge hollows or by means of continuous uniformly-dispersing pores is ofgreat consequence.

If the pressure of the gas exceeds 20 MPa, the gas often enters thespace between the molten resin surface and the mold surface, and largehollows are often formed, resulting in considerable increase in theincidence of defects in appearance such as silver marks and defects infunction such as lowered strength. In contrast, the gas injection in thepresent invention is employed for compensation of the deficiency ofexpansion, and a high pressure is not required.

In cooling of the molded article, the resin is preferably cooled aftermolding for a shorter time, while the gas is circulated and discharged.

A face material for covering the surface of the molded article in anintegrated manner may be applied onto the mold surface prior to molding.That is, the prior application of the face material onto the moldsurface provides a fiber-reinforced lightweight multi-layered resinmolded article. The face material is not particularly limited thereto,and a variety of materials may be used according to purpose and usage.Usable face materials include, for example, single-layered materialssuch as woven and non-woven fabrics, thermoplastic resin sheets, films,thermoplastic resin cellular sheets, and films printed with patterns andthe like; and multi-layered materials comprising a face material such asthermoplastic elastomer, or vinyl chloride resin, and a lining materialsuch as thermoplastic resin, or thermoplastic resin cellular sheet. Inthis case, the molded article may be covered entirely or partially withthe face material. In manufacture of a multi-layered molded articlecovered with a face material, depending on the properties of the facematerial; for example, in the case of a cushion face material or fiberface material, the face material is susceptible to damage due to thepressure of the injected resin under ordinary injection molding.Therefore, there is preferably employed an injection molding method inwhich resin is injected, in an amount insufficient to fill the volume ofa cavity, and a movable core is then advanced so as to compress theresin.

In the manufacturing method of the present invention, as the injectionmethod of injecting a fiber-containing molten resin into the moldcavity, there may be employed an ordinary method as well as a so-calledinjection compression molding method in which a fiber-containing moltenresin is injected into a cavity such that the cavity is incompletelyfilled with the resin, and a movable core is then advanced forcompression of the resin. In the case in which the molded article ismolded integrally with a face material of cellular sheets or fabrics,the injection compression molding which uses a low pressure to inject aresin is preferably used, in consideration of prevention of damages tothe face material at the time of injection.

Embodiments of modes of the present invention will next be describedwith reference to the drawings.

Embodiments of First Mode

FIG. 1 schematically shows a first embodiment of the method ofmanufacturing a fiber-reinforced lightweight resin molded articleaccording to the first mode of the present invention. FIG. 1(A) shows acondition immediately before injection of a fiber-containing moltenthermoplastic resin into an injection mold and subsequent expansion ofthe cavity of the injection mold. FIG. 1(B) shows a condition afterexpansion of the cavity of the injection mold and before opening of theinjection mold, i.e., a condition upon completion of forming of a moldedarticle. In FIG. 1(A), numeral 1 denotes a fixed mold; numeral 2 denotesa moving mold; numeral 3 denotes a movable core; numeral 4 denotes aprotruding portion of the moving mold 2; numeral 5 denotes a resinpassageway; numeral 6 denotes a cavity; numeral 7 denotes a gas inlet;and numeral 8 denotes a gas outlet. Upon start of the manufacture of thefiber-reinforced lightweight resin molded article of the present mode,the fixed mold 1 and the moving mold 2 having the protruding portion 4are clamped together. The movable core 3 is advanced into the cavity 6so as to determine a cavity volume for injection. Specifically, themovable core 3 is advanced to a position where a clearance D1 is definedin the thickness direction of a molded article as shown in FIG. 1(A). InFIG. 1(A), the tip of the protruding portion 4 is aligned with thesurface of the movable core 3. However, the positional relationshipbetween the tip and the surface may be determined as appropriateaccording to an expansion coefficient of a molded article and anexpansion coefficient of a portion of a molded article surrounding agrooved portion formed in the molded article. Similarly, the clearanceD1 and the shape of the movable core 3 may be determined as.appropriateaccording to the shape and a degree of lightness implementation of afinal molded article.

A fiber-containing molten thermoplastic resin is injected from thenozzle of an unillustrated plasticator into the cavity 6 in the aboveinitial state through the resin passageway 5. Cooling of the injectedmolten resin begins from a portion in contact with the mold. Before themolten resin is completely cooled and hardened, the movable core 3 isretracted as shown in FIG. 1(B). Specifically, the movable core 3 isretracted to a position corresponding to a clearance D2, i.e., to aposition where the cavity-volume is expanded to form a final moldedarticle. The retraction of the movable core 3 effects springback ofentangled fibers which are contained in the molten resin, therebycausing expansion of the molten resin into the shape of the final moldedarticle. In other words, the thus-generated expansion force causes themolten resin to be pressed against the mold surface and to be formedaccordingly. During molding, the protruding portion 4 of the moving mold2 remains still. As a result, a grooved portion corresponding to theprotruding portion 4 is formed in the molded article. After cooling, themold is opened, and the fiber-reinforced lightweight resin moldedarticle is taken out from the mold.

According to the present embodiment, the movable core 3 is advanced intothe cavity 6 in the thickness direction of the cavity 6, followed byinjection of the molten resin. Then, the movable core 3 is retracted toexpand the injected molten resin. Being projected into the cavity 6, theprotruding portion 4 functions to cool the molten resin as do the moldsurface and the surface of the movable core 3. Cooling of the moltenresin, or a reduction in temperature of the molten resin, causes anincrease in viscosity of the molten resin. Thus, a cooled region of themolten resin is substantially disabled or limited in its expansion ascompared to the remaining region of the molten resin. As a result, themolded article includes a coarse high-expansion region H1 and a denselow-expansion region L1. Because of the presence of the protrudingportion 4, the dense region L1 is formed not only along the periphery ofthe molded article but also along the grooved portion of the moldedarticle. The structure formed of the grooved portion and the surroundingdense region L1 functions like a ribbed structure, thereby yielding aneffect which would be yielded by the ribbed structure.

The present embodiment requires injection into the cavity 6 of a moltenresin having high expansibility, which depends on a required degree oflightness implementation of a molded article. Thus, as mentionedpreviously, fibers contained in an injected molten resin; for example,glass fibers, preferably have a long average length. Also, in order toobtain a molded article having a high porosity, a small amount of afoaming agent may be added to the material resin. The foaming agentcomplements an expansion force induced by springback phenomenon so as tobring the molten resin into close contact with the mold surface, therebypreventing the formation of sink marks. Also, after the movable core 3starts to retract, gas having a relatively low pressure of not higherthan 1 MPa may be introduced into the cavity 6 through the gas inlet 7while the gas outlet 8 is closed. Alternatively, gas may be releasedfrom the gas outlet 8 while a gas pressure at the gas outlet 8 ismaintained at a certain level. This promotes cooling of a molded articleand prevents the formation of sink marks on the surface of the moldedarticle. In contrast to isolated pores formed through use of a foamingagent for lightness implementation in a conventional method, poresformed in the fiber-reinforced lightweight resin molded article of thepresent invention are continuous by virtue of springback of entangledfibers which are contained in the molten resin. That is, pores arecontinuously formed along entangled fibers. Thus, the present inventionis characterized in that gas can be introduced -into a molded articlewhile homogenizing an expanded portion of the molded article. Throughintroduction of gas into the molded article, the molded article can becooled from inside as well, thus significantly shortening a moldingcycle. A region of a molded article surrounding the grooved portion,which is formed in a molded article by the protruding portion 4, is oflow expansion or non-expansion. In the case where gas is introduced intothe cavity 6, pores are preferably formed in a molded article in acontinuous manner throughout the molded article for permission of gasflow therethrough while the molded article has a low-expansion region.

FIG. 2 schematically shows a second embodiment of the method ofmanufacturing a fiber-reinforced lightweight resin molded articleaccording to the first mode of the present invention. The secondembodiment differs from the first embodiment of FIG. 1 in that when themovable core 3 is advanced, a side gap 9 is formed between the movingmold 2 and the movable core 3 and that the cavity 6 into which a moltenresin is injected is defined by the mold surface, the surface of themovable core 3, and the surface of the projecting portion 4. Uponinjection of a molten resin into the cavity 6, the molten resin ispressed under high pressure against the mold surface to thereby form amajor outer surface of a final molded article along the mold surface,and is also subjected to cooling through the mold surface and associatedsolidification to some degree. Accordingly, when the movable core 3 isretracted, the outer surface, particularly the side surface, of a moldedarticle is free of any adverse effect which would otherwise result fromretracting of the movable core 3. The second embodiment imparts betterappearance of the side surface to the molded article as compared to thefirst embodiment of FIG. 1.

FIG. 3 schematically shows a third embodiment of the method ofmanufacturing a fiber-reinforced lightweight resin molded articleaccording to the first mode of the present invention. The thirdembodiment differs from the second embodiment of FIG. 2 in that a facematerial 10 is previously attached to the surface of the fixed mold 1opposite the movable core 3. The third embodiment is adapted tomanufacture a molded article having the face material 10 integratedtherewith. Since the face material 10 is attached to the fixed mold 1, aside injection gate is employed for injection of a molten resin into thecavity 6. A molding method is substantially similar to that of thesecond embodiment except that the face material 10 is attached to thefixed mold 1; thus, the description thereof is omitted. Notably, in theabove-described embodiments, in order to advance and retract the movablecore 3, there is disposed, for example, a core-moving apparatus betweenthe moving mold 2 and a moving-mold attachment bed.

Embodiments of Second Mode

FIG. 4 schematically shows a first embodiment of the method ofmanufacturing a fiber-reinforced lightweight resin molded articleaccording to the second mode of the present invention. FIG. 4(A) shows acondition immediately before injection of a fiber-containing moltenresin into an injection mold and subsequent expansion of the cavity ofthe injection mold. FIG. 4(B) shows a condition after expansion of thecavity of the injection mold and before opening of the injection mold,i.e., a condition upon completion of forming of a molded article. InFIG. 4(A), numeral 11 denotes a fixed mold; numeral 12 denotes a movingmold; numeral 13 denotes a movable core having a plurality of coreheads; numeral 14 denotes a cavity; numeral 15 denotes a resinpassageway; numeral 16 denotes a gas inlet; and numeral 17 denotes a gasoutlet. Upon start of the manufacture of the fiber-reinforcedlightweight resin molded article of the present embodiment, the fixedmold 11 and the moving mold 12 are clamped together. The movable core 13having a plurality of core heads is advanced into the cavity 14 so as todetermine a cavity volume for injection.

Specifically, the movable core 13 is advanced to a position where aclearance D11 is defined in the thickness direction of a molded articleas shown in FIG. 4(A). The clearance D11 and the shape of the movablecore 13 may be determined as appropriate according to the shape and adegree of lightness implementation of a final molded article. Afiber-containing molten thermoplastic resin is injected from the nozzleof an unillustrated plasticator into the cavity 14 in the above initialstate through the resin passageway 15. Cooling of the injected moltenresin begins from a portion in contact with the mold. Before the moltenresin is completely cooled and hardened, the movable core 13is-retracted as shown in FIG. 4(B). Specifically, the movable core 13 isretracted to a position corresponding to a clearance D12, i.e., to aposition where the cavity volume is expanded to form a final moldedarticle. The retraction of the movable core 13 effects springback ofentangled fibers which are contained in the molten resin, therebycausing expansion of the molten resin into the shape of the final moldedarticle. In other words, the thus-generated expansion force causes themolten resin to be pressed against the mold surface and to be formedaccordingly. After cooling, the mold is opened, and the fiber-reinforcedlightweight resin molded article is taken out from the mold.

According to the present embodiment, the movable core 13 having aplurality of core heads is advanced into the cavity 14 in the thicknessdirection of the cavity 14, followed by injection of the molten resin.Then, the movable core 13 is retracted to expand the injected moltenresin. Being projected into the cavity 14, the core heads function tocool the molten resin as does the mold surface. Cooling of the moltenresin, or a reduction in temperature of the molten resin, causes anincrease in viscosity of the molten resin. Thus, a cooled region of themolten resin is substantially disabled or limited in its expansion ascompared to the remaining region of the molten resin. As a result, themolded article includes a coarse high-expansion region H2 and a denselow-expansion region L2. Because of the presence of the core heads, thedense region L2 is formed not only along the periphery of the moldedarticle but also in a central portion of the molded article of FIG.4(B). The central dense region L2 functions like a ribbed structure,thereby yielding an effect which would be yielded by the ribbedstructure.

The present embodiment requires injection into the cavity 14 of a moltenresin having high expansibility, which depends on a required degree oflightness implementation of a molded article. Thus, as mentionedpreviously, fibers contained in an injected molten resin; for example,glass fibers, preferably have a long average length. Also, in order toobtain a molded article having a high porosity, a small amount of afoaming agent may be added to a material resin. The foaming agentcomplements an expansion force of the injected molten resin so as tobring the molten resin into close contact with the mold surface, therebypreventing the formation of sink marks. Also, after the movable core 13starts to retract, gas having a relatively low pressure of not higherthan 1 MPa may be introduced into the cavity 14 through the gas inlet 16while the gas outlet 17 is closed. Alternatively, gas may be releasedfrom the gas outlet 17 while a gas pressure at the gas outlet 17 ismaintained at a certain level. This promotes cooling of a moldedarticle. In contrast to isolated pores formed through use of a foamingagent for lightness implementation in a conventional method, poresformed in the fiber-reinforced lightweight resin molded article of thepresent invention are continuous by virtue of springback of entangledfibers which are contained in the molten resin. That is, pores arecontinuously formed along entangled fibers. Thus, the present inventionis characterized in that gas can be introduced into a molded articlewhile homogenizing an expanded portion of the molded article. Throughintroduction of gas into the molded article, the molded article can becooled from inside as well, thus significantly shortening a moldingcycle.

The shape of a low-expansion region and that of a non-expansion regiondepend on the shape of a core head of the movable core. 13. Thelow-expansion and non-expansion regions may be of independent streaks,continuous streaks, grid, or any other shapes, which depend on the shapeof a molded article. In view of introduction of gas into a moldedarticle, pores are preferably formed in the molded article in acontinuous manner throughout the molded article for permission of gasflow therethrough while the molded article has a low-expansion region.

FIG. 5 schematically shows a second embodiment of the second mode of thepresent invention. As shown in FIG. 5, a face material 18 is previouslyattached to the surface of the fixed mold 11 opposite the movable core13 to thereby manufacture a molded article having the face material 18integrated therewith. Since the face material 18 is attached to thefixed mold 11, a side injection gate is employed for injection of amolten resin into the cavity 14. A molding method is substantiallysimilar to that of the first embodiment except that the face material 18is attached to the fixed mold 11; thus, the description thereof isomitted. Notably, in the above-described embodiments, in order toadvance and retract the movable core 13, there is disposed, for example,a core-moving apparatus between the moving mold 12 and a moving-moldattachment bed.

Embodiments of Third Mode

FIG. 6 schematically shows a first embodiment of the method ofmanufacturing a fiber-reinforced lightweight resin molded articleaccording to the third mode of the present invention. FIG. 6(A) shows acondition immediately before injection of a fiber-containing moltenresin into an injection mold and subsequent expansion of the cavity ofthe injection mold. FIG. 6(B) shows a condition after expansion of thecavity of the injection mold and before opening of the injection mold,i.e., a condition upon completion of forming of a molded article. InFIG. 6(A), numeral 21 denotes a fixed mold; numeral 22 denotes a movingmold; numeral 23 denotes a movable core; numeral 24 denotes a slitformed in the movable core 23; numeral 25 denotes a resin passageway;numeral 26 denotes a cavity; numeral 27 denotes a gas inlet; and numeral28 denotes a gas outlet. Upon start of the manufacture of thefiber-reinforced lightweight resin molded article of the presentembodiment, the fixed mold 21 and the moving mold 22 are clampedtogether. The movable core 23 is advanced into the cavity 26 so as todetermine a cavity volume for injection. Specifically, the movable core23 is advanced to a position where a clearance D21 is defined in thethickness direction of a molded article as shown in FIG. 6(A). Notably,in FIG. 6(A), the depth of the slit formed in the movable core 23 isidentical to the thickness of a final molded article. The clearance D21and the shape and quantity of the slit may be determined as appropriateaccording to the shape and a degree of lightness implementation of afinal molded article.

A fiber-containing molten resin is injected from the nozzle of anunillustrated plasticator into the cavity 26 in the above initial statethrough the resin passageway 25. Cooling of the injected molten resinbegins from a portion in contact with the mold. Particularly, the moltenresin which fills the slit shapes accordingly through quick cooling.Before other dominant molten resin is completely cooled and hardened,the movable core 23 is retracted as shown in FIG. 6(B). Specifically,the movable core 23 is retracted to a position corresponding to aclearance D22, i.e., to a position where the cavity volume is expandedto form a final molded article. The retraction of the movable core 23effects springback of entangled fibers which are contained in the moltenresin, thereby causing expansion of the molten resin into the shape ofthe final molded article. In other words, the thus-generated expansionforce causes the molten resin to be pressed against the mold surface andto be formed accordingly. Accordingly, the resin contained in the slitforms a dense region in which expansion of the resin is substantiallysuppressed, so that the porosity is low, and substantially no pores arecontained. In other words, the dense region forms a rib which connectsopposite skin layers. After cooling, the mold is opened, and thefiber-reinforced lightweight resin molded article is taken out from themold.

According to the present embodiment, the movable core 23 is advancedinto the cavity 26 in the thickness direction of the cavity 26, followedby injection or injection-and-compression of the molten resin. There iscooled the molten resin injected into the slit, which serves as part ofthe cavity 26. Then, the movable core 23 is retracted to expand theinjected molten resin. Cooling of the molten resin contained in theslit, or a reduction in temperature of the molten resin, causes anincrease in viscosity of the molten resin. Thus, the resin contained inthe slit is substantially disabled in its expansion. As a result, themolded article includes a coarse high-expansion region H3 (high-porosityregion), a dense peripheral region L3 (middle-porosity region), and ahighly dense region S3 (low-porosity region or non-pore region).

The present embodiment requires injection into the cavity 26 of a moltenresin having high expansibility, which depends on a required degree oflightness implementation of a molded article. Thus, as mentionedpreviously, fibers contained in an injected molten resin; for example,glass fibers, preferably have a long average length. Also, in order toobtain a molded article having a high porosity, a small amount of afoaming agent may be added to a material resin. The foaming agentcomplements an expansion force induced by springback phenomenon so as tobring the molten resin into close contact with the mold surface, therebypreventing the formation of sink marks. Also, after the movable core 23starts to retract, gas having a relatively low pressure of not higherthan 1 MPa may be introduced into the cavity 26 through the gas inlet 27while the gas outlet 28 is closed. Alternatively, gas may be releasedfrom the gas outlet 28 while a gas pressure at the gas outlet 28 ismaintained at a certain level. This promotes cooling of a molded articleand prevents the formation of sink marks on the surface of the moldedarticle. In contrast to isolated pores formed through use of a foamingagent for lightness implementation in a conventional method, poresformed in the fiber-reinforced lightweight resin molded article of thepresent invention are continuous by virtue of springback of entangledfibers which are contained in the molten resin. That is, pores arecontinuously formed along entangled fibers. Thus, the present inventionis characterized in that gas can be introduced into a molded articlewhile homogenizing an expanded portion of the molded article. Throughintroduction of gas into the molded article, the molded article can becooled from inside as well, thus significantly shortening a moldingcycle. In the present invention, pores are preferably formed in a moldedarticle in a continuous manner throughout the molded article forpermission of gas flow therethrough while the molded article has ahigh-expansion region, a low-expansion region, and a non-expansionregion.

FIG. 7 schematically shows a second embodiment of the method ofmanufacturing a fiber-reinforced lightweight resin molded articleaccording to the third mode of the present invention. The secondembodiment differs from the first embodiment of FIG. 6 in that when themovable core 23 is advanced, a side gap 29 is formed between the movingmold 22 and the movable core 23 and that the cavity 26 into which amolten resin is injected is defined by the mold surface, the surface ofthe movable core 23, and the slit 24. Upon injection of a molten resininto the cavity 26, the molten resin is pressed under high pressureagainst the mold surface to thereby form a major outer surface of afinal molded article along the mold surface, and is also subjected tocooling through the mold surface and associated solidification to somedegree. Accordingly, when the movable core 23 is retracted, the outersurface of a molded article is free of any adverse effect which wouldotherwise result from retracting of the movable core 23. The secondembodiment imparts better appearance of the side surface to the moldedarticle as compared to the first embodiment of FIG. 6. As shown in FIG.7, a face material 30 is previously attached to the surface of the fixedmold 21 opposite the movable core 23. The second embodiment is adaptedto manufacture a molded article having the face material 30 integratedtherewith. Since the face material 30 is attached to the fixed mold 21,a side injection gate is employed for injection of a molten resin intothe cavity 26. A molding method is substantially similar to that of thefirst embodiment except that the face material 30 is attached to thefixed mold 21; thus, the description thereof is omitted. Notably, in theabove-described embodiments, in order to advance and retract the movablecore 23, there is disposed, for example, a core-moving apparatus betweenthe moving mold 22 and a moving-mold attachment bed.

Embodiments of Fourth Mode

FIG. 8 schematically shows a first embodiment of the method ofmanufacturing a fiber-reinforced lightweight resin molded article havinga protruding portion according to the fourth mode of the presentinvention. FIG. 8(A) shows a condition immediately before injection of afiber-containing molten resin into an injection mold and subsequentexpansion of the cavity of the injection mold. FIG. 8(B) shows acondition after expansion of the cavity of the injection mold and beforeopening of the injection mold, i.e., a condition upon completion offorming of a molded article. In FIG. 8, numeral 31 denotes a fixed mold;numeral 32 denotes a moving mold; numeral 33 denotes a movable core;numeral 34 denotes a resin passageway; numeral 35 denotes a gas inlet;numeral 36 denotes a gas outlet; and numeral 37 denotes a cavity. Uponstart of the manufacture of the fiber-reinforced lightweight resinmolded article having a protruding portion of the present embodiment,the fixed mold 31 having grooved portions and the moving mold 32 areclamped together. The movable core 33 is advanced into the cavity 37 soas to determine a cavity volume for injection. Specifically, the movablecore 33 is advanced to a position where a clearance D31 is defined inthe thickness direction of a molded article as shown in FIG. 8(A). Theclearance D31 and the shape of the movable core 33 may be determined asappropriate according to the shape and a degree of lightnessimplementation of a final molded article.

A fiber-containing molten thermoplastic resin is injected from thenozzle of an unillustrated plasticator into the cavity 37 in the aboveinitial state through the resin passageway 34. Cooling of the injectedmolten resin begins from a portion in contact with the mold. Before themolten resin is completely hardened, the movable core 33 is retracted asshown in FIG. 8(B). Specifically, the movable core 33 is retracted to aposition corresponding to a clearance D31, i.e., to a position where thecavity volume is expanded to form a final molded article. The retractionof the movable core 33 effects springback of entangled fibers which arecontained in the molten resin, thereby causing expansion of the moltenresin into the shape of the final molded article. In other words, thethus-generated expansion force causes the molten resin to be pressedagainst the mold surface and to- be formed accordingly. Since thegrooved portions of the fixed mold 31 contain an additional molten resinin the thickness direction of a molded article and. since the moltenresin contained in the grooved portions are cooled quicker than the restof the molten resin injected into the cavity 37, the molten resincontained in the grooved portions is limited in its expansion duringexpansion of the cavity 37. As a result, the corresponding protrudingportions of a molded article, together with those regions of the moldedarticle which integrally extend from the protruding portions in thethickness direction of the molded article, form rib-like structures,thereby yielding an effect of ribs.

According to the present embodiment, the protruding portions are formedon a molded article in the thickness direction of the molded article.Thus, the protruding portions as well as a skin region of the moldedarticle are limited in its expansion when an injected molten resin isexpanded through retraction of the movable core 33. Depending on theshape and size of the protruding portions, the protruding portions andthose regions of the molded article which integrally extend from theprotruding portions in the thickness direction of the molded article aresubstantially disabled or limited (i.e., a low porosity) in itsexpansion as compared to the remaining region of the molten resin. As aresult, the molded article includes a general region H4 having a highporosity and a dense region L4 having a low porosity. The dense regionL4 is formed not only along the periphery of the molded article but alsoin the regions which extend from the protruding portions in thethickness direction of the molded article. The dense regions L4associated with the protruding portions function like a ribbedstructure, thereby yielding an effect which would be yielded by theribbed structure.

The present embodiment requires injection into the cavity 37 of a moltenresin having high expansibility, which depends on a required degree oflightness implementation of a molded article. Thus, as mentionedpreviously, fibers contained in an injected molten resin; for example,glass fibers, preferably have a long average length. Also, in order toobtain a molded article having a high porosity, a small amount of afoaming agent may be added to a material resin. The foaming agentcomplements an expansion force induced by springback phenomenon so as tobring the molten resin into close contact with the mold surface, therebypreventing the formation of sink marks. Also, after the movable core 33starts to retract, gas having a relatively low pressure of not higherthan 1 MPa may be introduced into the cavity 37 through the gas inlet 35while the gas outlet 36 is closed. Alternatively, gas may be releasedfrom the gas outlet 36 while a gas pressure at the gas outlet 36 ismaintained at a certain level. This promotes cooling of a molded articleand prevents the formation of sink marks on the surface of the moldedarticle.

In contrast to isolated pores formed through use of a foaming agent forlightness implementation in a conventional method, pores formed in thefiber-reinforced lightweight resin molded article having the protrudingportions of the present embodiment are continuous by virtue ofspringback of entangled fibers which are contained in the molten resin.That is, pores are continuously formed along entangled fibers. Thus, thepresent invention is characterized in that gas can be introduced into amolded article while homogenizing an expanded portion of the moldedarticle. Through introduction of gas into the molded article, the moldedarticle can be cooled from inside as well, thus significantly shorteninga molding cycle. Those regions of the molded article which integrallyextend from the protruding portions in the thickness direction of themolded article have a low porosity. In view of introduction of gas intoa molded article, pores are preferably formed in the molded article in acontinuous manner throughout the molded article for permission of gasflow therethrough while the molded article has the low-porosity regions.

FIG. 9 schematically shows a second embodiment of the method ofmanufacturing a fiber-reinforced lightweight resin molded article havinga protruding portion according to the fourth mode of the presentinvention. The second embodiment differs from the first embodiment ofFIG. 8 in that when the movable core 33 is advanced, a side gap 39 isformed between the moving mold 32 and the movable core 33 and that thecavity 37 into which a molten resin is injected is defined by thesurface of the moving mold 32, the surface of the movable core 33, andthe surface of the fixed mold 31 having grooved portions formed therein.Upon injection of a molten resin into the cavity 37, the molten resin ispressed under high pressure against the mold surface to thereby form amajor outer surface of a final molded article along the mold surface,and is also subjected to cooling through the mold surface and associatedsolidification to some degree. Accordingly, when the movable core 33 isretracted, the outer surface of a molded article is free of any adverseeffect which would otherwise result from retracting of the movable core33. The second embodiment imparts better appearance of the side surfaceto the molded article as compared to the first embodiment of FIG. 8.

FIG. 9 schematically shows a third embodiment of the method ofmanufacturing a fiber-reinforced lightweight resin molded article havinga protruding portion according to the fourth mode of the presentinvention. The third embodiment differs from the second embodiment ofFIG. 8 in that a face material 40 is previously attached to the surfaceof the fixed mold 31 opposite the movable core 33. The third embodimentis adapted to manufacture a molded article having the face material 40integrated therewith. A molding method is substantially similar to thatof the first embodiment except that the face material 40 is attached tothe fixed mold 31; thus, the description thereof is omitted.

FIG. 10 schematically shows a fourth embodiment of the method ofmanufacturing a fiber-reinforced lightweight resin molded article havinga protruding portion according to the fourth mode of the presentinvention. As shown in FIG. 10, grooved portions are formed in themoving mold 32; the moving mold 32 has a function of a movable core; andan auxiliary mold 41 biased by a spring 42 is employed. The cavity 37into which a molten resin is injected is defined by the fixed mold 31and the moving mold 32, which are clamped together, and the auxiliarymold 41. The mold structure of the present embodiment is. simplifiedthrough elimination of a movable core. Also, the present embodimentimproves the appearance of the side surface of a molded article. FIG.10(C) is a sectional view of the molded article of FIG. 10(B) andschematically shows a dense region L4 having a low porosity and a coarseregion H4 having a high porosity. In FIG. 10, the resin passagewayemploys a direct gate. However, through employment of a side gate, thetop surface of the molded article of FIG. 10(B) can have betterappearance, and, as needed, a face material can be integrally attachedto the top surface to thereby form a laminated molded article. Notably,in the above-described embodiments except that of FIG. 10, in order toadvance and retract the movable core 33, there is disposed, for example,a core-moving apparatus between the moving mold 32 and a moving-moldattachment bed.

EXAMPLES

Next, the advantages and effects of the present invention will bespecifically described by way of example. However, the present inventionis not limited thereto.

Examples 1 and 2 described below are drawn to embodiments according tothe first mode of the present invention.

Example 1

Glass fiber-reinforced polypropylene pellets (65 parts byweight)(containing 3 wt. % maleic anhydride-polypropylene) comprisingparallel-arranged glass fibers having a length of 12 mm in the amount of60 wt. %, and polypropylene pellets (35 parts by weight) having a meltindex of 30 g/10 min (MI: 230° C., under load of 2.16 kg) were dryblended, to thereby obtain molding material. An injection moldingmachine (clamping force: 850 t) comprising a screw having a compressionratio of 1.9 was employed in order to reduce the incidence of rupturingof the glass fibers. As shown in FIG. 2(A), while a movable core 3having protruding portions was thrust into a cavity 6 for clamping (aclearance D1 between a fixed mold and the protruding portions of themovable core was 4mm), the molding material was plasticized, weighed,and injected into the cavity. Two seconds after completion of chargingof the molding material, the movable core 3 was retracted to theposition as shown in FIG. 2(B) so that the molding material wasextended, expanded, and cooled, to thereby obtain a plate-shaped (600mm×300 mm) molded article having a thickness (D2) of 8 mm (a groovedportion: 4 mm×6 mm×240 mm). The molded article was cut out, and theexpansion was measured, showing an expansion coefficient of 2.0 at ahigh-expansion portion (H1). Also, the molded article was incinerated,and the mean fiber length of the remaining fibers was measured, andfound to be 7.2 mm. The inner circumferential edge, peripheral edge, andsurfaces of these edges of the grooved portion were formed of a denselayer having substantially no expansion. Especially, the grooved portionhas a function of a rib.

Example 2

Molding was performed by use of the molding material and injectionmolding machine used in Example 1, and the molds as shown in FIG. 3. Aface material (ten-fold foamed polypropylene/polyvinyl chloride leather:2 mm) was applied onto the surface of a fixed mold as shown in FIG.3(A), while a movable core was thrust; a molten resin was injected whilea clearance excluding the thickness of the face material (D1) wasadjusted to 2 mm; and the movable core was retracted to the positionwhere a thickness (D2) shown in FIG. 3(B) excluding the thickness of theface material is 12 mm so that the molten resin was extended andexpanded. Two seconds after the start of the retracting of the movablecore, nitrogen gas was charged, through a gas pin, under pressure of 0.8MPa for 30 seconds. After cooling, the molds were opened, and aplate-shaped (12 mm (excluding the thickness of the face material)×600mm×300 mm) molded article with the face material (a grooved portion: 10mm×8 mm×250 mm) was removed. The molded article was cut out, and theexpansion was measured, and an expansion coefficient of about 6 wasfound at a high-expansion portion (H1). Also, the molded article wasincinerated, and the mean fiber length of the remaining fibers wasmeasured, and found to be 6.9 mm. The inner circumferential edge,peripheral edge, and surfaces of these edges of the grooved portion wereformed of a strong layer having substantially no expansion. Especially,the grooved portion has a function of a rib.

Examples 3-7 and Comparative Example 1 described below are examplesAccording to the second mode of the present invention.

Example 3

Glass fiber-reinforced polypropylene pellets (65 parts by weight)(containing 3 wt. % maleic anhydride-polypropylene) comprisingparallel-arranged glass fibers having a length of 12 mm in the amount of60 wt. %, and polypropylene pellets (35 parts by weight) having a meltindex of 30 g/10 min (MI: 230° C., under load of 2.16 kg) were dryblended, to thereby obtain molding material. An injection moldingmachine (clamping force: 850 t) comprising a screw having a compressionratio of 1.9 was employed in order to reduce the incidence of rupturingof the glass fibers. As shown in FIG. 4(A), while a movable core 13 wasthrust into a cavity 14 for clamping (a clearance D11 between a fixedmold and the protruding portions of the movable core was 4mm), themolding material was plasticated, weighed, and injected into the cavity.Two seconds after completion of charging of the molding material, themovable core 13 was retracted to the position as shown in FIG. 4(B) sothat the molding material was extended, expanded, and cooled, to therebyobtain a molded article having a thickness (D12) of 12 mm. The moldedarticle was cut out, and the expansion was measured, showing that theportion of the molded article corresponding to the area which themovable portion of the movable core had been retracted was sufficientlyexpanded, but the circumferential portion and the portion which had beenpressed by the movable core at the time of clamping exhibited a lowexpansion coefficient (about 1.2) due to the cooling effect exerted bythe mold, so that they subsequently formed ribs.

Example 4

The preparation of molding material in Example 3was repeated except thata foaming agent (0.3 parts by weight)(EV-306G; manufactured by EiwaChemical Industry, Co., Ltd.) (in the form of a master batch containing30 wt. % foaming agent) was added to a mixture of the glassfiber-reinforced polypropylene pellets (50 parts by weight) andpolypropylene pellets (50 parts by weight) having a MI of 30 g/10 min.The molding in Example 3was repeated except that the clearance (D11) wasset to 3 mm when the movable core was thrust. The molded article was cutout, and the expansion was measured, showing that the portion of themolded article corresponding to the area which the movable portion ofthe movable core had been retracted was sufficiently expanded, but thecircumferential portion and the portion which had been pressed by themovable core at the time of clamping exhibited a low expansioncoefficient (about 1.2) due to the cooling effect exerted by the mold,so that they substantially formed rib structures.

Example 5

The procedure of Example 3was repeated except that the clearance (D11)was set to 2 mm when the movable core was thrust, a gas outlet wasclosed two seconds after the start of retracting of the movable core,and nitrogen gas was charged under a low pressure of 0.8 MPa. The moldedarticle was cut out, and the expansion was measured, showing that theportion of the molded article corresponding to the area which themovable portion of the movable core had been retracted was sufficientlyexpanded, but the circumferential portion and the portion which had beenpressed by the movable core at the time of clamping exhibited a lowexpansion coefficient (about 1.2) due to the cooling effect exerted bythe mold, so that they substantially formed rib structures.

Comparative Example 1

The procedure of Example 3was repeated except that glassfiber-reinforced polypropylene pellets comprising parallel-arrangedshort glass fibers (percentage of glass fiber: 40 wt. %) having a meanlength of 0.4mm was used as molding material. However, a slight ripplewas found at the tip end of the movable core, and substantially noexpansion was caused at the portion corresponding to the are which themovable portion of the movable core had been retracted.

Example 6

Molding was performed by use of the molding material and injectionmolding machine used in Example 3, and the molds as shown in FIG. 5. Aface material (ten-fold foamed polypropylene/polyvinyl chloride resinleather: 2 mm) was applied on the surface of a fixed mold as shown inFIG. 5(A) while a movable core was thrust; a molten resin was injectedwhile a clearance excluding the thickness of the face material (D1) wasadjusted to 4mm; and the movable core was retracted to the positionwhere a thickness (D2) shown in FIG. 5(B) excluding the thickness of theface material was 12 mm so that the molten resin was extended andexpanded. The molded article was cut out, and the expansion wasmeasured, showing that the portion of the molded article correspondingto the area which the movable portion of the movable core had beenretracted was sufficiently expanded, but the circumferential portion andthe portion which had been pressed by the movable core at the time ofclamping exhibited a low expansion coefficient (about 1.1) due to thecooling effect exerted by the mold, so that they substantially formedrib structures. Also, when the molded article integrally molded with aface material was bent, it exhibited very good rigidity. Further, whenthe molded article was partially compressed, no dents were formed in theface material.

Example 7

The molding of Example 6 was repeated except that a face material (sameas in Example 4: 3 mm) was applied onto the surface of a fixed mold asshown in FIG. 2(A) while a movable core was thrust; a molten resin wasinjected while a clearance excluding the thickness of the face material(D11) was adjusted to 2 mm; and the movable core was retracted to theposition where a thickness (D12) shown in FIG. 4(B) excluding thethickness of the face material was 12 mm so that the molten resin wasextended and expanded. Two seconds after the start of the retraction ofthe movable core, nitrogen gas was charged through a gas pin underpressure of 0.1 MPa. There were no sink marks on the surface of themolded article. The molded article was cut out, and the expansion wasmeasured, showing that the portion of the molded article correspondingto the area which the movable portion of the movable core had beenretracted was sufficiently expanded, but the circumferential portion andthe portion which had been pressed by the movable core at the time ofclamping exhibited a low expansion coefficient (about 1.1) due to thecooling effect exerted by the mold, so that they substantially formedrib structures. Also, when the molded article integrally molded with aface material was bent, it exhibited very good rigidity. Further, whenthe molded article was partially compressed, no dents were formed in theface material.

Examples 8-10 and Comparative Examples 2 and 3 described below areexamples according to the third mode of the present invention.

Example 8

Glass fiber-reinforced polypropylene pellets (70 parts by weight)(containing 3 wt. % maleic anhydride-polypropylene) comprisingparallel-arranged glass fibers having a length of 12 mm in the amount of70 wt. %, and polypropylene pellets (30 parts by weight) having a meltindex of 30 g/10 min (MI: 230° C., under load of 2.16 kg) were dryblended, to thereby obtain molding material. An injection moldingmachine (clamping force: 850 t) comprising a screw having a compressionratio of 1.9 was employed in order to reduce the incidence of rupturingof the glass fibers. As shown in FIG. 6(A), while a movable core 23having a slit 24 (width: 2 mm, depth: 7 mm) was thrust into a cavity 26for clamping (D21: 5 mm), the molding material was plasticated, weighed,and injected into the cavity. Three seconds after completion of chargingof the molding material, the movable core 23 was retracted to theposition as shown in FIG. 6(B) so that the molding material wasextended, expanded, and cooled, to thereby obtain a plate-shaped (600mm×300 mm) molded article having a thickness (D22) of 12 mm. The moldedarticle was cut out, and the expansion was measured, showing a porosityof about 58% at a high-expansion portion (H3) and substantially no poresat the slit portion. Also, the molded article was incinerated, and themean fiber length of the remaining fibers was measured, and found to be7.3 mm. The unexpanded portion of the slit portion had a rib structurewhich bridges the two skin layers.

Example 9

A molded article similar to that obtained in Example 8 was molded by useof the molding material and injection molding machine as used in Example8, and the molds as shown in FIG. 7; however, the face material as shownin FIG. 7 was not used in this example. A gap 29 between a movable core23 and a moving mold 22 was adjusted to 3 mm, while the movable corehaving a slit 4 (width: 2 mm, depth: 9 mm) was thrust; afiber-containing molten resin in the amount corresponding to the gap of3 mm was injected, while a cavity clearance (D21: 4mm) was increased by2 mm; and the movable core was advanced so as to compress-charge theresin. Three seconds after completion of the compression, the movablecore was retracted to the position where a cavity clearance D22 is 12 mmso as to extend and expand the resin. Meanwhile, two seconds after thestart of retracting of the movable core, nitrogen gas was chargedthrough a gas pin at 1 MPa into the molten resin. After cooling, themolds were opened, and the molded article was removed. The moldedarticle was cut out, and the expansion was measured, showing a porosityof about 75% at a high-expansion portion (H3), and substantially noexpansion or pores at the slit portion. Also, there were conspicuousunexpanded layers found at the peripheral edge of the molded article.Also, the molded article was incinerated, and the mean fiber length ofthe remaining fibers was measured, resulting in a value of 6.9 mm.

Example 10

A resin molded article integrally molded with a face material was moldedby use of the molding material, the injection molding machine and asimilar molded article as used in Example 8, and the mold as shown inFIG. 7. A face material (ten-fold foamed polypropylene/polyvinylchloride leather: 3 mm) was applied onto the surface of a fixed mold asshown in FIG. 7(A), while a movable core was thrust; a fiber-containingmolten resin in the amount corresponding to the clearance of 3 mm (D21)was injected, while a cavity clearance excluding the thickness of theface material was adjusted to 12 mm; and the movable core was advancedso as to compress the resin. Two seconds after compression-charging, themovable core was retreated to the position where a thickness (D22) shownin FIG. 7(B) excluding the thickness of the face material is 12 mm so asto extend and expand the resin. After cooling, the molds were opened,and a plate-shaped molded article having a thickness of 15 mm (excludingthe thickness of the face material) with the face material thereon wasobtained. The molded article was cut out, and the expansion wasinvestigated, showing a porosity of about 75% at a high-expansionportion (H3) and substantially no pores at the slit portion. Also, theface material was excellently integrated with the body portion, with theback surface being smooth and no warping, proving that the product wasan excellent lightweight molded product. Also, there were conspicuousunexpanded layers found at the peripheral edge of the molded article.Also, the molded article was incinerated, and the mean fiber length ofthe remaining fibers was measured, resulting in a value of 8.3 mm.

Comparative Example 2

The procedure of Example 8 was repeated except that resin pelletscomprising glass fibers having a mean length of 0.4 mm in an amount of40 wt. % was used as raw material resin. However, no molded article wasobtained since no expansion was caused.

Comparative Example 3

The procedure in Example 8 was repeated except that a foaming agent (6parts by weight)(EV-306G; manufactured by Eiwa Chemical Industry, Co.,Ltd.)(in the form of a 20 parts by weight of a master batch containing30 wt. % foaming agent) was added to material pellets (100 parts byweight), resulting a plate-shaped molded article. The molded article wascut out, and the expansion was investigated, showing that thehigh-expansion portion (H3) had a porosity of about 47% and a portioncorresponding to the slit portion had a porosity of about 15%. Inaddition, there were observed silver marks due to running of gas overthe entirety of the surface, and standing waves due to insufficientcooling.

Examples 11-12 described below are examples according to a fourth aspectof the present invention.

Example 11

Glass fiber-reinforced polypropylene pellets (65 parts by weight)(containing. 3 wt. % maleic anhydride-polypropylene) comprisingparallel-arranged glass fibers having a length of 12 mm in the amount of60 wt. %, and polypropylene pellets (35 parts by weight) having a meltindex of 30 g/10 min (MI: 230° C., under load of 2.16 kg) were dryblended, to thereby obtain molding material. An injection moldingmachine (clamping force: 850 t) comprising a screw having a compressionratio of 1.9 was employed in order to reduce the incidence of rupturingof the glass fibers. As shown in FIG. 8(A), while a movable core 33 wasthrust into a cavity 7 toward a fixed mold 31 having depressed portions(depth: 3 mm) for clamping (a clearance (D31) within the cavity 7 was 3mm), the molding material was plasticated, weighed, and injected intothe cavity. Two seconds after completion of charging of the raw resinmaterial, the movable core 33 was retreated to the position (D32) asshown in FIG. 8(B) so as to extend and expand the molding material.After cooling, there were obtained two plate-shaped (300 mm×600 mm)molded articles having a thickness of 9 mm (a protruding portion: 3 mm(height)×300 mm×20 mm). The molded article was cut out, and formation ofpores was investigated, showing that a flat portion (H4) had a porosityof about 67% and a region (L4) corresponding to the protruding portionhad a porosity of about 26% indicating a dense structure. The moldedarticle was incinerated, and the mean fiber length of the remainingfibers was measured, resulting in a value of 7.2 mm. The molded articlehad excellent surface appearance, high rigidity, and high resistance tobuckling.

Example 12

A resin molded article integrally molded with a face material was moldedby use of the molding material and injection molding machine as used inExample 11, and the molds as shown in FIG. 10. A face material (ten-foldfoamed polypropylene/polyvinyl chloride leather: 2 mm) was applied ontothe surface of a movable core 33; a fiber-containing molten resin in theamount corresponding to the gap of 3 mm was injected, while a cavityclearance was adjusted to 10 mm; and 2 seconds after starting ofinjection, the movable core 33 was advanced so as to compress the resin(FIG. 11(A)). Two seconds after the compression, the movable core 33 wasretreated to the position where a thickness (D32) shown in FIG. 10(B)was 12 mm so as to extend and expand the resin. Meanwhile, 1.5 secondsafter the start of the retreat of the movable core, nitrogen gas wascharged, through a gas pin, under pressure of 0.8 MPa for 40 seconds.After cooling, the molds were opened, to thereby obtain two plate-shaped(300 mm×600 mm) molded articles having a thickness of 12 mm (excludingthe thickness of the face material)(the protruding portion: 3 mm(height)×300 mm×20 mm). The molded article was cut out, and formation ofpores was investigated, showing that a flat portion (H) had a porosityof about 75% and a region (L4) corresponding to the protruding portionhad a porosity of about 41%. The molded article was incinerated, and themean fiber length of the remaining fibers was measured, resulting in avalue of 8.6 mm. The molded article had excellent surface appearance,high rigidity, and high resistance to buckling.

What is claimed is:
 1. A method of manufacturing a fiber-reinforcedresin molded article having a grooved portion formed in the moldedarticle, which method comprises the steps of injecting afiber-containing molten thermoplastic resin into a mold cavity formedwithin a mold having a movable core which can advance and retractrelative to the mold cavity and also having a protruding portion forforming a grooved portion in the molded article; and retracting themovable core toward the direction in which the capacity of the moldcavity is expanded.
 2. The method of manufacturing a fiber-reinforcedresin molded article according to claim 1, which method comprisesinjecting a fiber-containing molten thermoplastic resin into a moldcavity formed by a fixed mold, a movable mold having a protrudingportion for forming a grooved portion of the molded article, and amoving core capable of advancing and retracting within the moving mold.3. The method of manufacturing a fiber-reinforced resin molded articleaccording to claim 1, wherein at the time of injection a part of themold cavity is defined by a gap between the protruding portion of themoving mold and a movable core.
 4. The method of manufacturing afiber-reinforced resin molded article according to claim 1, wherein agas is injected into the interior of the fiber-reinforced lightweightresin molded article within the mold cavity.
 5. The method ofmanufacturing a fiber-reinforced resin molded article according to claim4, wherein a fiber-containing molten thermoplastic resin is injectedinto the mold cavity on the surface of which a face material is appliedin advance.
 6. The method of manufacturing a fiber-reinforced resinmolded article according to claim 4 or 5, wherein the fiber-containingmolten thermoplastic resin is obtained by plasticizing and meltingfiber-containing thermoplastic resin pellets having a length of 2-100 mmand contains parallel-arranged fibers having the same length in anamount of 20-80 wt. % with respect to the weight of the resultantresin-fiber mixture, or obtained by plasticizing and melting a mixtureof the pellets and other pellets containing the fibers so that theamount of fibers is 10-70 wt. % with respect to the weight of theentirety of the mixture.